FIG. 4 is a side view showing a conventional spot welding robot. In FIG. 4, 51 denotes a 6-axis vertical articulated robot, 52 denotes a spot welding gun attached to the tip of the vertical articulated robot 51, and 53 denotes a cable for supplying a welding current to the spot welding gun.
The vertical articulated robot 51 includes a fixing portion 54, a turning portion 55 supported pivotally on the fixing portion 54 and turned around a vertical axis, a lower arm 56 supported pivotally on the turning portion 55 and rocked in a longitudinal direction, an upper arm 57 supported pivotally on the lower arm 56 and rocked in a vertical direction, and a wrist portion 58 attached to the tip of the upper arm 57. The wrist portion 58 has the degree of freedom of a rotation around three axes which are orthogonal to each other and has the spot welding gun 52 fixed to a tip thereof.
The cable 53 is wired from a welding timer, which is not shown, to the fixing portion 54 and is clamped onto the fixing portion 54 where said cable is wound around the vertical axis (in a counterclockwise direction seen from above) at the level of the fixing portion 54 and rises up to the level of the turning portion 55. Furthermore, the cable 53 is wound around the vertical axis (in a clockwise direction seen from above) at the level of the turning portion 55 and is clamped onto the turning portion 55. Furthermore, the cable 53 rises upward along the lower arm 56, and is hung on a cable stand 59 fixed onto the upper arm 57 and is extended to the spot welding gun 52.
In the conventional spot welding robot, however, the cable 53 is lifted dynamically above the upper arm 57 with providing certain looseness. Therefore, there is a problem in that the cable 53 interferes with a peripheral apparatus or the like. Moreover, there is a problem in that the cable 53 is rubbed with the peripheral apparatus or the like and is thus worn out. Furthermore, there is also a problem in that the operation of the wrist portion 58 is limited if the looseness of the cable is decreased to avoid the interference with the peripheral apparatus or the like.
Although the cable 53 provided to have the looseness above the upper arm 57 is rocked according to the operation of the robot where said rocking motion is difficult to be predicted with accuracy. Therefore, another problem is that the interference of the cable with the peripheral apparatus cannot be checked in the simulation such as by offline teaching.